I. Field of the Invention
This invention relates to a syringe having means to perform aspiration.
II. Description of Related Art
A conventional syringe has a barrel with a plunger in slidable and sealing engagement therein, and a needle attached to one end of the barrel. An injection using a conventional syringe is performed by inserting the needle of the syringe into a vial of injectant. The plunger of the syringe is then withdrawn while the user grips the barrel of the syringe with their other hand. This draws the injectant into the barrel of the syringe. The user may then check for any air bubbles in the injectant in the barrel, caused by air being inadvertently drawn into the barrel, and remove them in the usual way through the needle. The injection can then be performed.
The injection is administered by inserting the needle through the skin of a patient. It is necessary to check the position of the needle tip within the patient to ensure the injectant is delivered appropriately, such as to a muscle or into a blood vessel. This is achieved by aspiration of the syringe, which involves withdrawing the plunger a small amount once the needle is within the patient. This will cause the body material adjacent the needle tip to be drawn into the syringe barrel through the needle where the user can view it. Thus, if the injectant is intended for a blood vessel for example, if blood is drawn into the syringe then the needle tip is in the correct position for the injection to be delivered. If blood is not observed, the user would need to find an alternative injection site.
As can be appreciated, the aspiration procedure may be painful for the patient and also potentially hazardous. In particular, as the user is required to pull on the plunger while the needle is within a patient, this can cause unwanted movement of the needle tip, which may be painful. This is particularly so as, due to the seal the plunger needs to have with the barrel of the syringe, withdrawal of the plunger may require the application of a significant force thereby reducing the chance of keeping the syringe still. The position of the needle tip may also move during aspiration and therefore the injectant may not be delivered to the intended location. Thus, although the user may have thought that an appropriate injection site had been found by aspirating the syringe, the action of aspiration may cause the needle tip to move, which may render the injection ineffective or even dangerous to the health of the patient.